1. Field of the Invention
The present invention relates to a directional coupler, and more specifically, to a directional coupler including a spiral-shaped main line and a spiral-shaped sub-line that are embedded in a laminated body.
2. Description of the Related Art
As a directional coupler of the related art, for example, a laminated type directional coupler described in Japanese Unexamined Patent Application Publication No. 2010-11519 is known. Hereinafter, the laminated type directional coupler described in Japanese Unexamined Patent Application Publication No. 2010-11519 will be described. FIG. 11 is the exploded view of a laminated type directional coupler 500 described in Japanese Unexamined Patent Application Publication No. 2010-11519.
As illustrated in FIG. 11, the laminated type directional coupler 500 includes dielectric sheets 502a to 502g, a main line 504, and a sub-line 506. The main line 504 includes a vortex-shaped first coupling line portion 504a and a vortex-shaped second coupling line portion 504b that are connected to one another. The first coupling line portion 504a and the second coupling line portion 504b are provided on dielectric sheets 502b and 502e, respectively. On the other hand, the sub-line 506 includes a vortex-shaped first coupling line portion 506a and a vortex-shaped second coupling line portion 506b that are connected to one another. The first coupling line portion 506a and the second coupling line portion 506b are provided on dielectric sheets 502c and 502f, respectively. In addition, the first coupling line portion 504a and the first coupling line portion 506a are electromagnetically coupled to one another, and the second coupling line portion 504b and the second coupling line portion 506b are electromagnetically coupled to one another. The laminated type directional coupler 500 configured in such a manner as described above is mounted on a circuit substrate so that a surface on a lower side in a lamination direction defines a mounting surface.
In the laminated type directional coupler 500 described in Japanese Unexamined Patent Application Publication No. 2010-11519, it is necessary to discriminate the direction of the laminated type directional coupler 500 at the time of being mounted to the circuit substrate. In more detail, the laminated type directional coupler 500 can be mounted so that the main line 504 defines a main line and the sub-line 506 defines a sub-line, and furthermore, can be mounted to the circuit substrate so that the main line 504 defines a sub-line and the sub-line 506 defines a main line. However, as described below, there is a problem in that the characteristics of the laminated type directional coupler 500 fluctuate.
The main line 504 is provided on an upper side in the lamination direction, as compared to the sub-line 506. In more detail, the first coupling line portion 504a is provided on an upper side in the lamination direction, as compared to the first coupling line portion 506a, and the second coupling line portion 504b is provided on an upper side in the lamination direction, as compared to the second coupling line portion 506b. Therefore, stray capacitance occurring between a wiring line or a ground conductor within the circuit substrate and the main line 504 is less than stray capacitance occurring between the wiring line or the ground conductor within the circuit substrate and the sub-line 506. Accordingly, the characteristics of the laminated type directional coupler 500 when the main line 504 defines a sub-line and the sub-line 506 defines a main line are different from those when main line 504 defines a main line and the sub-line 506 defines a sub-line. Therefore, in the laminated type directional coupler 500, it is necessary to discriminate the direction of the laminated type directional coupler 500 at the time of being mounted to the circuit substrate.
Therefore, a direction recognition mark (not illustrated) is provided on the surface (for example, the back surface of a dielectric sheet 502g) of the laminated type directional coupler 500 of the related art. By the mounting apparatus recognizing this direction recognition mark, the laminated type directional coupler is mounted on the circuit substrate in a desired direction. However, there is a problem in that the formation of the directional mark complicates the manufacturing process for the laminated type directional coupler. In addition, since it is necessary to mount the laminated type directional coupler to the circuit substrate after the direction thereof has been discriminated, there is also a problem in that the time required for the directional coupler to be mounted to the circuit substrate is increased.